1. Technical Field of Field of Invention
The present invention relates generally to the field of heat transfer and, more specifically, to a direct-interface, fusible heat sink for non-venting, regenerable and self-contained thermal regulation.
2. Description of the Prior Art
Astronaut cooling during extravehicular activity (EVA) is a critical design issue in developing a portable life support system that meets the requirements of a space station mission. Some of the requirements are that the cooling device be easily regenerable and non-venting during operation.
During EVA, a crew member generates metabolic energy, while portable life support systems and equipment produce additional heat. Ninety percent of metabolic energy is in the form of waste heat that must be removed from the body during the EVA to allow crew comfort and performance. Once removed from the body, the heat may be either stored or rejected, or both.
On orbit, heat rejection occurs only by radiation or mass transfer. Heat storage may be accomplished by inducing a phase change in a substance or by causing an endothermic reaction to take place. Any self-contained system that attempts to control the thermal condition of an astronaut wearing a space suit will be limited by either capacity or rate of heat transfer. For example, a storage system will be limited by capacity, as will a mass transfer system. A radiation system will be limited by heat-transfer rate.
Thermal regulation of astronauts during EVA has been accomplished in the past by use of a sublimator or an umbilical coolant supply. These systems provide adequate capacity and rate and are compact and light weight. However, they have disadvantages in that they require venting and subsequent loss of water during operation. Also, the umbilicals are awkward and difficult to manage.
Future exploration missions will require an EVA system that can provide routine, possibly daily, operation that continues for months without support or resupply from surface-based resources or facilities. For these reasons, it is desirable for a thermal regulation system to be easily regenerable, non-venting, and extremely reliable. Some specific requirements are that the total capacity be about 11,680 Btu (3,420 W-hr) for an 8 hr EVA and that the device be able to cool at 2,000 Btu/hr (585.6 W) for 15 minutes any time during this 8 hr period. More specific requirements are listed below in Table 1:
TABLE 1 ______________________________________ Design and Performance Requirements ______________________________________ EVA duration 8 hr EVA environment LEO (any orientation) Environment load 0 Btu/hr (0 W) Metabolic heat load Minimum 400 Btu/hr (117 W) Average 1000 Btu/hr (293 W) Maximum 2000 Btu/hr (5686 W) PLSS heat load Average, 635 Btu/hr (186 W) Net Heat Load Minimum 635 Btu/hr (186 W) 8-hr average 1500 Btu/hr (439 W) 15-min max 2000 Btu/hr (586 W) Total heat capacity 11680 Btu (3420 W) Cooling garment temperatures Minimum 60.degree. F. (15.5.degree. C.) (5) Maximum 85.degree. F. (29.4.degree. C.) Heat-sink outlet temperature &lt;40.degree. F. (4.4.degree. C.) (humidity control) Regeneration time Less than 16 hr EVA frequency 8 hr/day, 6 day/Wk Mission duration 6 mo Operational lifetime &gt;1228 hr ______________________________________
While there has been a number of astronaut cooling devices that use fusible heat sinks, none has demonstrated a direct interface between the cooling liquid transport loop and the phase-change material. Moreover, all the previous designs have incorporated conventional heat exchangers.